Distinguishing prehistoric human influence on late-Holocene forests in southern Ontario, Canada

Abstract

The influence of Native Americans on late-Holocene forests of North America remains a contentious issue, as it is unclear whether vegetation transitions inferred from pollen records are a product of prehistoric human disturbance. In southern Ontario, the adoption of maize agriculture coincides with neoglacial cooling, so distinguishing the relative roles of prehistoric people and climatic change in shaping forest composition requires that pollen records be interpreted in a regional context. In this study, we objectively identify pollen records from the southern Ontario region which exhibit periods of significant pre-European anthropogenic disturbance in the context of the archeological record. This enables a comparison of pollen records shaped primarily by climatic cooling with those disturbed by prehistoric human forest clearance. Our results suggest that regional-scale late-Holocene cooling resulted in a gradual and synchronous shift from deciduous to boreal taxa. However, forest clearance by Native Americans resulted in a secondary succession characterized by the replacement of late-successional beech-maple forest with ruderal species, grasses and poplar, followed by mid-successional oak and white pine. This transition consistently coincides in space and time with an increase in archeological records of human occupation. The method we have developed here to distinguish significant prehistoric human impacts could be applied to pollen records in other regions, or on a continental scale.

Multi‐decadal drought and amplified moisture variability drove rapid forest community change in a humid region

“…A large spike in microscopic charcoal is synchronous with the final drought at Irwin Smith, after which beech populations never recovered to pre-MCA levels. The lack of recovery of beech populations after about 700 BP may have been related to severe beech mortality during the large fires, drought-or temperature-related pathogen infestation (Harvell et al 2002), or onset of a cooler and perhaps wetter climate regime (Munoz and Gajewski 2010) that favored recruitment of hemlock and other species over beech (Fig. 2B).…”

Used planet: A global history

“…69). Agriculture developed 4,000-5,000 y ago in the savanna habitats of Africa (70), India (71), Southeast Asia (72), and the North American forests and savannas (73,74). Although some pathways led from sedentary hunter-gatherers to early farmers, as in Southwest Asia or Yangtze China (68), others shifted from mobile hunting to the addition of herding first, for example in Africa (70), or from mobile hunting and gathering to mobile forms of agriculture like shifting cultivation, as in India (75), New Guinea (76), or South America (77).…”

“…Widespread agricultural land use by midHolocene is further evidenced by altered fire regimes that may have transformed vegetation structure and species composition across many regions, with woodland ecosystems from the Mediterranean to the Tropics increasingly recognized as the bio-cultural legacies of long histories of prior human use (50,74,(78)(79)(80)(81)(82)(83)(84). Another general legacy of agricultural land use has been the creation of anthropogenic soils (anthrosols) (85), including the manure-enriched "plaggen" soils of Northwestern Europe, which may date to 4000 B.C.…”

“…By the 1500s and even earlier in some regions of Asia and Europe, agricultural productivity had reached remarkable levels through intensive use of a wide variety of highly developed technologies, including irrigation, multiple cropping, crop rotations incorporating legumes, and a wide range of fertilizers, including manures, ashes, and even commercially traded oil seed cakes (44,92). In less densely populated regions, agricultural productivity was generally much lower, as in the pre-and postcolonial Americas, Australia, and New Zealand (44,45,74). Agricultural yields within the most densely populated and productive preindustrial land-use systems compared well with modern yields and were sustained in some regions for centuries to millennia, even though they also tended to require extreme inputs of labor and other socially unsustainable hardships (43)(44)(45)92).…”

Spatiotemporal distribution of Holocene populations in North America

“…For example, frequency distributions have been used to estimate continental-scale population growth in North America (North America here means the United States and Canada, the extent of our database) over the past 15 ka using the Canadian Archaeological Radiocarbon Database (CARD) (2,3). Regional studies in North America have highlighted the impacts of environmental change on population size using these methods and documented the impact of human activities on the vegetation (1,(6)(7)(8)(9)(10). Although some studies have attempted to investigate between-region demographic changes for particular time periods (11) or map the point distribution for certain time intervals (3), the spatiotemporal distribution of demographic growth through the Holocene in North America after the arrival of humans has not been tracked at a continental scale.…”